JP2013202935A - Inkjet recording method, ultraviolet curable ink, and inkjet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet recording method excelling in curability, and capable of preventing generation of curing crease.SOLUTION: An inkjet recording method includes: a discharge process of discharging ultraviolet curable ink containing (meth)acrylic esters containing a vinyl ether group onto a recording object medium S; and a curing process of irradiating the ultraviolet curable ink landed on the recording object medium with an ultraviolet ray from an ultraviolet light emitting diode where peak intensity of the ultraviolet ray emitted therefrom is ≥800 mW/cmto cure the ink.

Description

  The present invention relates to an ink jet recording method, an ultraviolet curable ink, and an ink jet recording apparatus.

  Conventionally, various methods have been used as a recording method for forming an image on a recording medium such as paper based on an image data signal. Among these, the ink jet system is an inexpensive apparatus, and ink is ejected only to a required image portion to form an image directly on a recording medium. Therefore, the ink can be used efficiently, and the running cost is low. Furthermore, the inkjet method is excellent as a recording method because of its low noise.

  In recent years, in order to form an image having excellent water resistance, solvent resistance, and scratch resistance on the surface of a recording medium, an ultraviolet curable ink that is cured when irradiated with ultraviolet rays in an ink jet recording method has been used. ing.

  For example, Patent Document 1 discloses C.I. I. 15% by weight of a pigment blue 15: 4 dispersion, 62.55% by weight of propoxylated neopentyl glycol diacrylate (SR9003), 13% by weight of 2- (2-vinyloxyethoxy) ethyl acrylate (VEEA), 0.83% by weight of polymerization inhibitor, 6% by weight of photopolymerization initiator, 2.5% by weight of ethyl-4- (dimethylamino) benzoate, and 0.1% by weight of polyether-modified polydimethylsiloxane as a wetting agent A recording method is disclosed in which an ultraviolet curable ink-jet ink composed of the above is discharged from a print head having a nozzle density and an outer diameter as predetermined values, and is irradiated with ultraviolet rays (Example 1 of Patent Document 1).

International Publication No. 2011/039081

  However, if the recording method disclosed in Patent Document 1 is used to produce a cured film, that is, a cured ink coating film, from an ultraviolet curable inkjet ink, the following problems occur.

  First, when the thickness of the cured film is relatively thin, oxygen inhibition is affected in the case of a radical polymerization reaction system, resulting in poor curability. Therefore, the film must be thickened to the extent that oxygen inhibition does not occur at the time of printing, resulting in a problem that the print image quality is deteriorated. On the other hand, when the thickness of the cured film is relatively large, the pigment has a strong tendency to absorb a part of the ultraviolet rays, so that the coating film discharged onto the recording medium is completely cured even when the ultraviolet rays are irradiated. Since the energy required for this is insufficient, the vicinity of the surface of the coating may be cured first, resulting in incomplete curing of the interior of the coating or may require time for curing. And when the uncured ink existing inside the coating film is cured, the vicinity of the previously cured surface is wrinkled, or the ink flows irregularly before the ink inside the coating film is cured. As a result, wrinkles (hereinafter also referred to as “cured wrinkles”) occur on the surface of the coated film after curing. Due to the cured wrinkles, there arises a problem that the film properties of the coating film are inferior.

  Accordingly, an object of the present invention is to provide an ink jet recording method that is excellent in curability and can prevent the occurrence of curing wrinkles.

  Another object of the present invention is to provide an ultraviolet curable ink used in the recording method and an ink jet recording apparatus using the recording method.

As a result of intensive studies to solve the above problems, the present inventors have ejected an ultraviolet curable ink containing a predetermined vinyl ether group-containing (meth) acrylic acid ester onto a recording medium, and then cured the ink. Sometimes, the peak intensity of the irradiated ultraviolet light (hereinafter also referred to as “irradiation peak intensity”) is excellent in curability of the recorded matter obtained by irradiating the ultraviolet light from the ultraviolet light emitting diode having 800 mW / cm ² or more. And it discovered that a hardening wrinkle could be prevented effectively and completed this invention.

That is, the present invention is as follows.
[1]
A discharge step including discharging an ultraviolet curable ink containing a vinyl ether group-containing (meth) acrylic acid ester represented by the following general formula (I) onto a recording medium;
A curing step including irradiating the ultraviolet curable ink landed on the recording medium with ultraviolet rays from an ultraviolet light emitting diode having a peak intensity of ultraviolet rays of 800 mW / cm ² or more, and curing the ink; An ink jet recording method comprising:
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)
[2]
The inkjet recording method according to [1], wherein the irradiation energy of ultraviolet rays emitted from the ultraviolet light emitting diode is 100 to 600 mJ / cm ² .
[3]
In the curing step, before irradiating ultraviolet rays from the ultraviolet light emitting diode having a peak intensity of 800 mW / cm ² or more, the emission peak wavelength is in the range of 360 to 420 nm, and the peak intensity of the irradiated ultraviolet rays is 800 mW. [1] or [2] further comprising irradiating an ultraviolet ray having an irradiation energy of 50 mJ / cm ² or less from an ultraviolet light emitting diode that generates an ultraviolet ray that is less than / cm ² to temporarily cure the ultraviolet curable ink. ] The inkjet recording method as described in.
[4]
The inkjet recording method according to any one of [1] to [3], wherein recording is performed using a line inkjet recording apparatus including a line head having a length equal to or longer than a width of a recording medium.
[5]
The inkjet recording method according to any one of [1] to [4], wherein the irradiation from the ultraviolet light-emitting diode is independently at least one of pulse irradiation and spot irradiation by a condenser lens.
[6]
The inkjet recording method according to [1] or [2], wherein a peak intensity of the irradiated ultraviolet ray is in a range of 800 to 4,000 mW / cm ² .
[7]
The inkjet recording method according to [1] or [2], wherein the ultraviolet light emitting diode has an emission peak wavelength in a range of 360 to 420 nm.
[8]
An ultraviolet curable ink used in the inkjet recording method according to any one of [1] to [7].
[9]
An ink jet recording apparatus using the ink jet recording method according to any one of [1] to [7].

It is a block diagram which shows the structure of a line printer. FIG. 2 is a schematic view around a recording area in one embodiment of the line printer of FIG. 1. It is sectional drawing which showed typically a part among examples of UV-LED with a lens among 1st irradiation parts. It is the schematic of the recording region periphery in the other aspect of the line printer of FIG. It is a wave form diagram of the electric current sent through UV-LED in the printer of one Embodiment of this invention when not performing pulse irradiation of an ultraviolet-ray. It is a wave form diagram of the pulse current sent through UV-LED in the printer of one embodiment of the present invention in the case of performing pulse irradiation of ultraviolet rays.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. In addition, this invention is not restrict | limited to the following embodiment, A various deformation | transformation can be implemented within the range of the summary. Moreover, in each drawing used for the following description, the scale is appropriately changed for each component in order to make each component (member) recognizable on the drawing. The present embodiment is not limited only to the ratio of the number, shape, and size of the components and the relative positional relationship of the components described in these drawings.

In this specification, “curability” refers to a property of curing in response to light. The “cured wrinkle” means wrinkles generated on the surface of the cured coating as described above. “Abrasion resistance” refers to the property that when the cured product is rubbed, the cured product is difficult to peel off and scratch. “Ejection stability” refers to the property of ejecting stable ink droplets from a nozzle without clogging the nozzle. “Bleed” means bleeding, and “bleed resistance” refers to the property of preventing bleeding at the edge of an image. “Storage stability” refers to the property that the viscosity before and after storage is difficult to change when the ink is stored.
In the present specification, “(meth) acrylate” means at least one of acrylate and its corresponding methacrylate, “(meth) acryl” means at least one of acrylic and its corresponding methacryl, “(Meth) acryloyl” means at least one of acrylic and methacryl corresponding thereto.

[Inkjet recording apparatus]
One embodiment of the present invention relates to an inkjet recording apparatus, that is, a printer. The recording apparatus uses an inkjet recording method described later. FIG. 1 is a schematic view of the vicinity of a recording area in one embodiment of a line printer.

  Examples of the printer include a line printer and a serial printer, but these have different printer methods. Briefly speaking, the line printer has a line head having a length equal to or longer than the width of the recording medium, preferably a length corresponding to the width of the recording medium (recording medium width). The head is fixed without moving (almost) and printing is performed in one pass (single pass). On the other hand, a serial printer normally performs printing in two or more passes (multi-pass) while the head reciprocates (shuttle movement) in a direction orthogonal to the conveyance direction of the recording medium. In this embodiment, any type of printer can be used.

  Among these, a line printer (line ink jet recording apparatus) forms an image only by scanning a recording medium once in a predetermined direction (hereinafter referred to as “conveying direction”), as will be described later. For this reason, the line printer is preferable because the printing speed is significantly higher than that of the serial printer. However, there is a problem that the ink discharge amount per pass is large and curing wrinkles are easily generated. Therefore, the present embodiment capable of preventing the occurrence of curing wrinkles exhibits a remarkable effect particularly for a line printer. Hereinafter, a description will be given with reference to FIGS. 1 and 2.

  The printer 1 is a recording device that forms an image on a recording medium, and is communicably connected to a computer 110 that is an external device.

  A printer driver is installed in the computer 110. The printer driver is a program for displaying a user interface on a display device (not shown) and converting image data output from an application program into print data (image formation data). This printer driver is recorded on a “computer-readable recording medium” such as a flexible disk FD or a CD-ROM. Alternatively, the printer driver can be downloaded to the computer 110 via the Internet. In addition, this program is comprised from the code | cord | chord for implement | achieving various functions.

  Then, the computer 110 outputs print data corresponding to the image to the printer 1 in order to cause the printer 1 to form an image.

  Here, the “recording apparatus” in this specification means an apparatus that forms an image on a recording medium, and corresponds to, for example, the printer 1. The “recording control device” means a device that controls the recording device, and corresponds to, for example, the computer 110 in which a printer driver is installed.

The printer 1 according to this embodiment is an apparatus that forms an image on a recording medium by discharging ultraviolet curable ink that is cured by irradiation with ultraviolet rays. The ultraviolet curable ink contains at least a predetermined vinyl ether group-containing (meth) acrylic acid ester, and is cured by a polymerization reaction caused by irradiation with ultraviolet rays.
The specific ink composition of the ultraviolet curable ink will be described later.

  The printer 1 according to this embodiment includes a transport unit 20, a head unit 30, an irradiation unit 40, a detector group 50, and a controller 60. The printer 1 that has received the print data from the computer 110 as an external device controls each unit, that is, the transport unit 20, the head unit 30, and the irradiation unit 40 by the controller 60, and places it on the recording medium S according to the print data. Form an image. The controller 60 controls each unit based on the print data received from the computer 110 and forms an image on the recording medium S. The situation in the printer 1 is monitored by the detector group 50, and the detector group 50 outputs the detection result to the controller 60. The controller 60 controls each unit based on the detection result output from the detector group 50.

The transport unit 20 is for transporting the recording medium S in the transport direction. As shown in FIG. 2, the transport unit 20 includes, for example, an upstream transport roller 23 </ b> A and a downstream transport roller 23 </ b> B, and a belt 24. When a transport motor (not shown) rotates, the upstream transport roller 23A and the downstream transport roller 23B rotate, and the belt 24 rotates. The recording medium S fed by a paper feed roller (not shown) is conveyed by the belt 24 to a recordable area (area facing the head). As the belt 24 transports the recording medium S, the recording medium S moves in the transport direction with respect to the head unit 30. The recording medium S that has passed through the recordable area is discharged to the outside by the belt 24.
Note that the recording medium S being conveyed is electrostatically attracted or vacuum attracted to the belt 24. In addition, although the term “paper feeding” is used here for convenience, a recording medium described later can be used as the recording medium in the present embodiment.

  The head unit 30 is for ejecting ultraviolet curable ink toward the recording medium S. The head unit 30 forms dots on the recording medium S by discharging each ink onto the recording medium S being conveyed, thereby forming an image. The printer 1 of this embodiment is a line printer, and each head of the head unit 30 can form dots corresponding to the width of the recording medium at a time. Specifically, as shown in FIG. 2 which is a schematic diagram of the periphery of the recording area in one embodiment of the line printer of FIG. 1, the white ink head W, the black ink head K, and the cyan ink head are sequentially arranged from the upstream side in the transport direction. In the case where each of C, magenta ink head M, and yellow ink head Y is provided, each head has dots corresponding to the width of the recording medium S from the back to the front of the paper (the direction perpendicular to the transport direction). A plurality are arranged so as to be discharged. In this way, each head is controlled from the upstream side, and dots are formed at necessary positions in one line corresponding to the width of the recording medium S, so that the recording medium S is scanned once in the transport direction. An image can be formed.

  The white ink head W is an ultraviolet curable white ink ejection unit. The black ink head K is an ultraviolet curable black ink ejection unit. The cyan ink head C is an ultraviolet curable cyan ink ejection unit. The magenta ink head M is an ultraviolet curable magenta ink discharge unit. The yellow ink head Y is a discharge portion for ultraviolet curable yellow ink.

  The irradiation unit 40 irradiates ultraviolet rays toward the dots of the ultraviolet curable ink landed on the recording medium S. The dots formed on the recording medium S are cured by being irradiated with ultraviolet rays from the irradiation unit 40. The irradiation unit 40 in this embodiment may be provided with the 1st irradiation parts 42a-42e and the 2nd irradiation part 44, as shown in FIG.

The first irradiation units 42a to 42e irradiate ultraviolet rays for temporarily curing the dots formed on the recording medium. The first irradiation units 42a to 42e are disposed in front of the second irradiation unit 44 where curing is performed, that is, upstream in the transport direction. To position. Here, “temporary curing” is also referred to as pinning, which means temporary fixing of ink, and more specifically, curing for preventing bleeding between dots and controlling the dot diameter. Therefore, it is sufficient that at least a part of the dots (droplets), for example, the dot surface is cured.
In the following, in order to distinguish from temporary curing, the final curing, that is, curing by irradiating ultraviolet rays from an ultraviolet light emitting diode (UV-LED) having an irradiation peak intensity of 800 mW / cm ² or more is referred to as “main”. Also called “curing”.

  The first irradiation units 42a to 42e are provided on the downstream side in the transport direction of the white ink head W, the black ink head K, the cyan ink head C, the magenta ink head M, and the yellow ink head Y, respectively. That is, the first irradiation unit is provided for each ink color.

The first irradiation units 42a to 42e include ultraviolet light emitting diodes (UV-LEDs) as light sources for ultraviolet irradiation. The UV-LED can easily change the irradiation energy by controlling the magnitude of the input current. The UV-LED is a type having a condensing lens (hereinafter also referred to as “LED with lens”), and the irradiation energy is maintained by condensing and irradiating a limited irradiation region from the LED with lens. However, spot irradiation can be performed with a higher irradiation peak intensity.
Hereinafter, the LED with lens will be described. FIG. 3 is a cross-sectional view schematically showing a part of an example of the UV-LED with a lens in the first irradiation unit.

The UV-LED 72 is mainly composed of a UV-LED chip 72a that emits ultraviolet rays and a condenser lens 72b. The ultraviolet rays issued by the UV-LED chip 72a are condensed by the condenser lens 72b to form a fixed irradiation angle. Irradiation is directed downward of the first irradiation unit. The condensing lens 72b is a package that covers the UV-LED chip 72a, and includes a lens whose surface is formed in a hemispherical shape and a cover that protects the surface, and hemispherical ultraviolet light emitted from the UV-LED chip 72a. The light is condensed toward the center line. The material for the lens and the cover is not limited to the following, but for example, a transparent resin such as glass, silicon resin, and silicon rubber can be used. The structure of the lens is not limited to that described above, and any lens that can collect light may be used. For example, the lens is not molded into a hemisphere integrally with a package, but a separate hemispherical lens is attached. It may be a thing. The UV-LED chip 72a included in the irradiation unit 40 has a supply current value controlled by a UV-LED driving circuit (not shown) controlled by the controller 60, and can be switched between an on state and an off state instantaneously. Then, it is possible to irradiate ultraviolet rays having an irradiation intensity necessary for temporarily curing the uncured ultraviolet curable ink attached to the recording medium S. A large number of UV-LEDs are arranged in a line in the width direction and the transport direction of the recording medium S to constitute each first irradiation unit. Positioning the UV-LEDs arranged in a row in the transport direction of the recording medium S between the width directions of the UV-LEDs arranged in a row in the width direction of the recording medium S causes the UV-LEDs to be condensed. It is preferable in that the irradiated area can be evenly dispersed in the width direction in the transport direction.
For other matters relating to the UV-LED unit, for example, FIG. 4 disclosed in JP 2010-23285A and the description thereof may be referred to. Moreover, the irradiation energy of temporary curing by the first irradiation units 42a to 42e, the emission peak wavelength, and the irradiation peak intensity will be described later.

  The second irradiating unit 44 irradiates the dots formed on the recording medium S with ultraviolet rays for curing (substantially) completely, that is, main curing. The second irradiation unit 44 is provided downstream of the yellow ink head Y in the transport direction. Further, the length of the second irradiation unit 44 in the width direction of the recording medium S is equal to or larger than the width of the recording medium S. Then, the second irradiation unit 44 irradiates the dots formed by each head of the head unit 30 with ultraviolet rays.

The 2nd irradiation part 44 of this embodiment is equipped with UV-LED as a light source of ultraviolet irradiation. Since the UV-LED has been described in the first irradiation units 42a to 42e, the description thereof is omitted here. Here, lamps such as metal halide lamps, xenon lamps, carbon arc lamps, chemical lamps, low-pressure mercury lamps, and high-pressure mercury lamps can also be used as the light source. However, the irradiation with the lamp has a light emission wavelength up to a short wavelength, so that the inside is irradiated and curing wrinkles are not generated. On the other hand, heat generation, size (including a cooling device), power consumption, and life of the light source, and an irradiator Problems arise in various ways, such as the cost of Further, the UV-LED is extremely superior in that it is small in size, has a long life, generates little heat, has high efficiency, and can reduce costs.
The irradiation energy of the main curing by the second irradiation unit 44, the emission peak wavelength, and the irradiation peak intensity will be described later.

  The detector group 50 includes a rotary encoder (not shown), a paper detection sensor (not shown), and the like. The rotary encoder detects the rotation amount of the upstream side conveyance roller 23A and the downstream side conveyance roller 23B. The transport amount of the recording medium S can be detected based on the detection result of the rotary encoder. The paper detection sensor detects the position of the tip of the recording medium S being fed.

  The controller 60 is a control unit (control unit) for controlling the printer. The controller 60 includes an interface unit 61, a CPU 62, a memory 63, and a unit control circuit 64. The interface unit 61 transmits and receives data between the computer 110 that is an external device and the printer 1. The CPU 62 is an arithmetic processing unit for controlling the entire printer. The memory 63 is for securing an area for storing a program of the CPU 62, a work area, and the like, and includes storage elements such as a RAM and an EEPROM. The CPU 62 controls each unit via the unit control circuit 64 in accordance with a program stored in the memory 63.

[Modification of Inkjet Recording Device]
The printer 1 shown in FIG. 1 described above is merely an example of the ink jet recording apparatus according to the present invention, and various variations exist.
First, each of the first irradiation units 42a to 42e and the second irradiation unit 44 in FIG. 2 may be either for temporary curing or main curing. For example, when the white ink is ejected from the white ink head W located upstream in the conveyance direction in FIG. 2 for the purpose of imparting excellent shielding properties to the image and a solid pattern image is formed, the first irradiation unit 42a is the main irradiation unit 42a. It is good that it is an irradiation part for hardening.
Moreover, the main curing by irradiation with ultraviolet rays having an irradiation peak intensity of 800 mW / cm ² or more may be performed once or twice or more. In particular, when the main curing is performed twice or more, there may be two or more second irradiation parts 44.
Further, the order of the ink heads of the respective colors shown in FIG. 2 may be changed in any way, and in addition to this, one or more of the ink heads are not provided, or provided but not operated. Also good. Furthermore, in addition to the ink heads of the respective colors shown in FIG. 2, another ink head (the color may be the same as or different from the existing one) may be provided. You may replace with the ink head of another color.
Hereinafter, various embodiments of the present embodiment will be described as modified examples. However, the present embodiment is not limited to these modified examples.

  The recording apparatus according to the first modification is the printer 1 that does not include or does not operate the second irradiation unit 44 described above. According to the first modified example, one or more irradiation units among the first irradiation units 42a to 42e may perform the main curing instead of the second irradiation unit 44, and the temporary curing described above may not be performed (first (When 1 irradiation part 42a-42e performs all hardening).

  The recording apparatus according to the second modification is the printer 1 that does not include or does not operate one or more of the first irradiation units 42a to 42e. According to the second modified example, the temporary curing described above may not be performed (when the first irradiation units 42a to 42e are not provided or provided but are not operated).

The recording apparatus according to the third modified example includes a white ink head W, a black ink head K, a cyan ink head C, a magenta ink head M, a yellow ink head Y, and a first ink jetting head provided downstream in the transport direction of these heads. It is the printer 1 provided with the 1st irradiation part provided in one or more heads and the conveyance direction downstream among 1 irradiation parts 42a-42e. FIG. 4 shows an aspect of the third modified example, and is a schematic view around the recording area in another aspect of the line printer of FIG. The line printer shown in FIG. 1 includes a black ink head K, a first irradiation unit 42b, and a second irradiation unit 44 in order from the upstream side in the transport direction.
Note that the printer 1 of the third modified example does not include the second irradiation unit 44 as in the first modified example described above, or includes the first irradiation unit 44 but does not operate, or the first irradiated unit similar to the second modified example described above. 42a to 42e may not be provided or may be provided but not operated.

The recording apparatus according to the fourth modified example includes a white ink head W, a white ink temporary curing irradiation unit, a cyan ink head C, a cyan ink temporary curing irradiation unit, a magenta ink head M, in order from the upstream side in the transport direction. Magenta ink temporary curing irradiation section, black ink head K, black ink temporary curing irradiation section, yellow ink head Y, first main curing irradiation section, clear ink head CL, and second main curing irradiation. And a recording apparatus provided with a unit. According to the recording apparatus according to the fourth modification, it is possible to realize excellent shielding by using white ink as a base and improving image quality by overcoating with clear ink (transparent ink). In addition, the color ink can be fully cured before the clear ink is ejected by irradiating ultraviolet rays from the main curing irradiation unit before and after the clear ink is ejected from the clear ink head CL.
The recording apparatus according to the fourth modification may not include at least one of the white ink head W, the white ink temporary curing irradiation unit, and the clear ink head CL, or the main curing irradiation unit. May be included (preferably including the second main curing irradiation unit).

  The recording apparatus according to the fifth modification is of a type that does not have a condenser lens (hereinafter also referred to as “lens-less LED”) as a UV-LED that is an ultraviolet radiation source, instead of the above-described LED with lens. I have. The LED without lens is the same as the LED with lens except that it does not have the condenser lens 72b in FIG. In an example of the lensless LED, the surface of the package covering the UV-LED chip 72a of FIG. 3 is formed into a flat surface instead of a hemisphere, and the cover for protecting the surface is also flat.

  In the recording apparatus according to the sixth modification, an input current to at least one of the first irradiation units 42a to 42e and the second irradiation unit 44 is turned on and off by a UV-LED drive circuit (not shown). Are repeatedly switched to a pulse current to perform ultraviolet pulse irradiation (hereinafter, the LED is also referred to as “pulse irradiation LED”). As a driving circuit for the pulse irradiation LED, a MOFSET circuit for performing PWM control can be used. FIG. 5A is a waveform diagram of a current passed through the UV-LED in the printer according to the present embodiment when ultraviolet pulse irradiation is not performed. FIG. 5B is a waveform diagram of a pulse current that flows through the UV-LED in the printer of this embodiment in the case of performing pulsed irradiation of ultraviolet rays. In the case of a pulse current, the input current is a peak input current that is a current at the peak of the pulse. The total amount of power input to the UV-LED is calculated by the following mathematical formula.

Total power amount = input voltage × T1 × Duty ratio In the above formula, the irradiation time (T1) to the recording medium is the time from the start of irradiation to the recording medium to the end of irradiation. The duty ratio is a value represented by the following formula when the pulse is driven for one period.

Duty ratio = duration when current is on / (duration when current is on + duration when current is off)
The duty ratio in the case of an LED that does not perform pulse irradiation is 1. The duty ratio in the case of performing pulse irradiation may be 0.5, for example, and the pulse frequency may be 1 kHz, for example. The heat generation of the UV-LED generally increases as the total amount of power increases.

  In general, the irradiation peak intensity of the UV-LED increases as the input current increases. By performing pulse irradiation as shown in FIG. 5b, the irradiation peak intensity can be further increased while maintaining the total input current amount when the time T1 from the start of irradiation to the end of irradiation is fixed. it can. Thus, since pulse irradiation LED increases an irradiation peak intensity | strength efficiently, it is especially suitable for using with the 2nd irradiation part 44 for which bigger irradiation peak intensity is required. Pulse irradiation LED may be used also in the 1st irradiation parts 42a-42e, and when performing this hardening instead of temporary hardening, it is preferable that the said 1st irradiation part also uses pulse irradiation LED.

  For such a pulse irradiation LED, for example, refer to FIGS. 1 and 2 disclosed in Japanese Patent Application Laid-Open No. 2006-231795, the description thereof, and the matters disclosed in Japanese Translation of PCT International Publication No. 2011-523370. The irradiation energy of the pulse irradiation LED can be calculated using the following mathematical formula.

Irradiation energy = irradiation peak intensity × T1 × Duty ratio Therefore, when T1 is fixed, the peak intensity can be increased while maintaining the same irradiation energy of the LED in the case where the pulse irradiation is not performed, or The irradiation energy of the LED can be reduced while maintaining the same peak intensity.

  In addition, it is preferable that the irradiation from UV-LED, especially the irradiation for performing main curing rather than temporary curing is at least one of said pulse irradiation and said spot irradiation. In this case, as described above, the irradiation peak intensity can be further increased while maintaining the irradiation energy.

[Inkjet recording method]
One embodiment of the present invention relates to an inkjet recording method. The ink jet recording method can use the ink jet recording apparatus of the above embodiment. The ink jet recording method uses a vinyl ether group-containing (meth) acrylic acid ester (hereinafter, also simply referred to as “vinyl ether group-containing (meth) acrylic acid ester”) represented by the following general formula (I). A discharge step including discharging the contained ultraviolet curable ink onto a recording medium, and a peak intensity of ultraviolet rays irradiated to the ultraviolet curable ink landed on the recording medium is 800 mW / cm ² or more. And a curing step including curing the ink by irradiating ultraviolet rays from an ultraviolet light emitting diode (UV-LED).

[Discharge process]
In the ejection step, the viscosity of the ink during ejection is preferably 25 mPa · s or less, more preferably 5 to 20 mPa · s. If the viscosity of the ink is as described above with the temperature of the ink at room temperature or without heating the ink, the ink may be discharged at room temperature or without heating the ink. On the other hand, the ink may be discharged at a predetermined value by heating the ink to a predetermined temperature. In this way, good discharge stability is realized.

  Since the ultraviolet curable ink has a higher viscosity than the water-based ink used in a normal inkjet ink, the viscosity fluctuation due to the temperature fluctuation during ejection is large. Such fluctuations in the viscosity of the ink have a great influence on the change in the droplet size and the change in the droplet discharge speed, which can cause image quality deterioration. Therefore, it is preferable to keep the temperature of the ink during ejection as constant as possible.

[Curing process]
Next, in the curing step, the ink ejected on the recording medium is irradiated with ultraviolet rays (light) from the second irradiation unit 44, or from the first irradiation units 42a to 42e in the case of performing main curing instead of temporary curing. ) Is cured by irradiation. In other words, the ink coating film formed on the recording medium becomes a cured film when irradiated with ultraviolet rays. This is because the photopolymerization initiator that can be contained in the ink is decomposed by irradiation with ultraviolet rays to generate starting species such as radicals, acids, and bases, and the polymerization reaction of the photopolymerizable compound depends on the function of the starting species. It is to be promoted. Or it is because the photopolymerization reaction of a polymeric compound starts by irradiation of an ultraviolet-ray. At this time, if a sensitizing dye is present together with the photopolymerization initiator in the ink, the sensitizing dye in the system absorbs active ultraviolet rays to be in an excited state and contacts the photopolymerization initiator to decompose the photopolymerization initiator. It can be accelerated and a more sensitive curing reaction can be achieved.

  The superiority of using the UV-LED as the light source (ultraviolet light source) is as described above.

The emission peak wavelength during the irradiation is preferably in the range of 360 to 420 nm, and more preferably in the range of 380 to 410 nm. When the emission peak wavelength is within the above range, it is preferable because the UV-LED is easily available and inexpensive.
Note that the emission peak wavelength may be one or plural within the preferable wavelength range. Even in the case where there are a plurality, the total irradiation energy amount of the ultraviolet light having the emission peak wavelength is set as the irradiation energy.

Peak intensity of ultraviolet rays irradiated by the (irradiated peak intensity) is a 800 mW / cm ² or more, preferably 1,000 mW / cm ² or more. When the irradiation peak intensity is within the above range, the curability is excellent and the generation of curing wrinkles can be effectively prevented. More specifically, it effectively prevents the surface of the ink coating from being cured first and curing wrinkles as a result of the internal curing of the ink coating being delayed compared to the surface curing. Can do.

The irradiation peak intensity will be further described. An LED has a narrow emission wavelength range due to its characteristics. Among them, a long wavelength LED having an emission peak wavelength in the range of 360 to 420 nm as described above is inexpensive, but has only a limited emission wavelength range of a long wavelength. Therefore, it is difficult for the irradiated ultraviolet rays to reach the inside of the ink droplets that have landed on the recording medium, and only the surface of the ink coating film is cured first. Therefore, there is a tendency for hardened wrinkles to occur. Thus, the present inventors have found that by setting the irradiation peak intensity to 800 mW / cm ² or more, curing wrinkles can be reduced even when a long wavelength LED is used. On the other hand, an ultraviolet curable ink containing a vinyl ether group-containing (meth) acrylic acid ester represented by the following general formula (I) as a polymerizable compound has a high curing speed, and in particular, has a limited emission peak such as an LED. A large curing rate can also be obtained by ultraviolet irradiation from a light source having a wavelength. However, when the ink is used, there is a problem that curing wrinkles are likely to occur. Even when such an ink is used, the present inventor can obtain a high-quality recorded matter having excellent curability and no cured wrinkles by setting the irradiation peak intensity to 800 mW / cm ² or more. They found out. When such an ink is used and the irradiation peak intensity is small, the cause of curing wrinkles is that such an ink has a fast curing speed on the surface of the coating film, but has a perfect effect inside the coating film. Presumed to be slow. But the cause is not limited to this.

Here, the ultraviolet irradiation with an irradiation peak intensity of 800 mW / cm ² or more may be performed once or twice or more. Moreover, when performing said ultraviolet irradiation twice or more, you may irradiate ultraviolet rays from the same light source several times, and you may perform ultraviolet irradiation one or more times from a different light source, respectively.

Moreover, since the irradiation peak intensity can suppress the cost of the irradiator and can prevent the heat generated from the light source and the leakage light from affecting the head, the discharge stability is excellent. preferably 4,000 mW / cm ^2, more preferably 800~2,000mW / cm ^2, more preferably 1,000~2,000mW / cm ^2.

  In addition, the irradiation peak intensity | strength in this specification employ | adopts the value measured using the ultraviolet-ray intensity meter UM-10 and the light-receiving part UM-400 (all are Konica Minolta Sensing, Inc. (KONICA MINOLTA SENSING, INC. Product)). . However, this does not mean that the measurement method of the irradiation peak intensity is limited, and a conventionally known measurement method can be used.

Moreover, 100-600 mJ / cm < ² > is preferable, as for the irradiation energy in the case of said irradiation, 200-600 mJ / cm < ² > is more preferable, 200-500 mJ / cm < ² > is further more preferable. When the irradiation energy is within the above range, excellent curability can be obtained, and the cost of the irradiation unit necessary for irradiation can be suppressed.

  In addition, the irradiation energy in this specification is calculated by multiplying the time from the start of irradiation to the end of irradiation by the irradiation peak intensity, and in the case of a pulse irradiation LED, it is further calculated by multiplying the duty ratio.

Here, the ultraviolet irradiation with the irradiation peak intensity of 800 mW / cm ² or more may be performed a plurality of times. In this case, said irradiation energy is represented by the irradiation energy amount which totaled multiple times of irradiation. In addition, in the case where irradiation with an irradiation peak intensity of 800 mW / cm ² or more is performed a plurality of times, the irradiation energy in the first irradiation after discharge is preferably 800 mJ / cm ² or less, because discharge stability is good, and is preferably 400 mJ / cm ² or less. cm ² or less is more preferable, 200 mJ / cm ² or less is more preferable, and 50 to 200 mJ / cm ² is even more preferable.

  When the irradiation peak intensity, irradiation energy, and emission peak wavelength described above are within preferable ranges, curing at low energy and high speed is possible due to the composition of the ink described later. Further, the irradiation time can be shortened by the composition of the ink described later, and in this case, the printing speed is increased. On the other hand, the irradiation peak intensity can be reduced by the composition of the ink, which will be described later. In this case, the apparatus can be downsized and the cost can be reduced.

Further, in the curing step, it is preferable to perform the above-described temporary curing before performing the main curing by irradiating ultraviolet rays from the UV-LED having an irradiation peak intensity of 800 mW / cm ² or more as described above. In the temporary curing stage, ultraviolet light (light) is irradiated to the ultraviolet curable ink described later from the first irradiation portions 42a to 42e for temporary curing.

Irradiation peak intensity from UV-LED at the stage of the preliminary curing is preferably less than 800 mW / cm ^2, more preferably from 500 mW / cm ² or less, more preferably 100~500mW / cm ^2. Further, the irradiation energy at the stage of the preliminary curing is preferably at 50 mJ / cm ² or less, and more preferably 10~50mJ / cm ^2. When the irradiation peak intensity and the irradiation energy are within the above ranges, the irradiation light source having the irradiation peak intensity of 800 mW / cm ² or more can be arranged away from the head, and heat generation or leakage light from the light source is generated in the head. Can be prevented and the bleed resistance is excellent.

Furthermore, when multi-color printing of multi-color ink by a plurality of heads is performed using the recording apparatus as shown in FIG. 1 above, the minimum irradiation for preventing color mixing is performed for each head, and finally, By collectively irradiating multicolor inks with an intensity of 800 mW / cm ² or more, the cost of the light source can be kept extremely low.

  The emission peak wavelength in the pre-curing stage is preferably in the range of 360 to 420 nm, more preferably in the range of 380 to 410 nm, for the same reason as the irradiation energy in the irradiation.

[Recording medium]
A recorded matter is obtained by ejecting ink onto a recording medium using the ink jet recording method of the present embodiment. Examples of the recording medium include an ink absorbing or non-absorbing recording medium. The ink jet recording method of this embodiment can be widely applied to recording media having various absorption performances, from non-absorbing recording media in which ink penetration is difficult to absorbent recording media in which ink penetration is easy.

  The absorbent recording medium is not particularly limited. For example, plain paper such as electrophotographic paper having high ink permeability, ink jet paper (an ink absorbing layer composed of silica particles or alumina particles, or polyvinyl alcohol ( Art paper, coated paper, etc. used for general offset printing with relatively low ink permeability, such as PVA) and polyvinyl pyrrolidone (PVP). Examples include cast paper.

  The non-absorbable recording medium is not particularly limited. For example, films and plates of plastics such as polyvinyl chloride, polyethylene, polypropylene, and polyethylene terephthalate (PET), and metals such as iron, silver, copper, and aluminum are used. Examples thereof include a plate, a metal plate produced by vapor deposition of these various metals, a plastic film, a plate made of an alloy such as stainless steel or brass.

  As described above, according to this embodiment, the inkjet is excellent in curability, can effectively prevent curing wrinkles, and can also have excellent abrasion resistance, ejection stability, and bleed resistance. A recording method can be provided.

[UV curable ink]
One embodiment of the present invention relates to an ultraviolet curable ink. The ultraviolet curable ink is used in the ink jet recording method of the above embodiment.
Hereinafter, additives (components) contained in or that can be contained in the ultraviolet curable ink of the present embodiment (hereinafter also simply referred to as “ink”) will be described.

(Polymerizable compound)
The polymerizable compound contained in the ink can be polymerized at the time of light irradiation alone or by the action of a photopolymerization initiator described later, and the printed ink can be cured.

(Vinyl ether group-containing (meth) acrylic acid esters)
The ink in this embodiment contains vinyl ether group-containing (meth) acrylic acid esters represented by the following general formula (I) as a polymerizable compound.
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.)

  When the ink contains the vinyl ether group-containing (meth) acrylic acid esters, the ink can have excellent curability, and the ink can also have a low viscosity. In addition, it is better to use a compound having both a vinyl ether group and a (meth) acryl group in one molecule than to use a compound having a vinyl ether group and a compound having a (meth) acryl group separately. It is preferable for improving curability.

In the above general formula (I), the divalent organic residue having 2 to 20 carbon atoms represented by R ² is a linear, branched or cyclic substituted having 2 to 20 carbon atoms. May be an alkylene group, an optionally substituted alkylene group having an oxygen atom by an ether bond and / or an ester bond in the structure, and an optionally substituted divalent alkylene group having 6 to 11 carbon atoms. Aromatic groups are preferred. Among these, C2-C6 alkylene groups such as ethylene group, n-propylene group, isopropylene group, and butylene group, oxyethylene group, oxy n-propylene group, oxyisopropylene group, and oxybutylene group An alkylene group having 2 to 9 carbon atoms having an oxygen atom due to an ether bond in the structure is preferably used.

In the above general formula (I), the monovalent organic residue having 1 to 11 carbon atoms represented by R ³ is a linear, branched or cyclic substituted having 1 to 10 carbon atoms. Suitable alkyl groups and optionally substituted aromatic groups having 6 to 11 carbon atoms are preferred. Among these, C6-C2 aromatic groups, such as a C1-C2 alkyl group which is a methyl group or an ethyl group, a phenyl group, and a benzyl group, are used suitably.

  When each of the organic residues is an optionally substituted group, the substituent is divided into a group containing a carbon atom and a group not containing a carbon atom. First, when the substituent is a group containing a carbon atom, the carbon atom is counted in the carbon number of the organic residue. Examples of the group containing a carbon atom include, but are not limited to, a carboxyl group and an alkoxy group. Next, examples of the group not containing a carbon atom include, but are not limited to, a hydroxyl group and a halo group.

  Examples of the vinyl ether group-containing (meth) acrylic acid esters include, but are not limited to, for example, 2-vinyloxyethyl (meth) acrylate, 3-vinyloxypropyl (meth) acrylate, and 1-methyl (meth) acrylate. 2-vinyloxyethyl, 2-vinyloxypropyl (meth) acrylate, 4-vinyloxybutyl (meth) acrylate, 1-methyl-3-vinyloxypropyl (meth) acrylate, 1-vinyloxymethyl (meth) acrylate Propyl, 2-methyl-3-vinyloxypropyl (meth) acrylate, 1,1-dimethyl-2-vinyloxyethyl (meth) acrylate, 3-vinyloxybutyl (meth) acrylate, 1-methyl- (meth) acrylate 2-vinyloxypropyl, 2-vinyloxybutyl (meth) acrylate, (meth) a 4-vinyloxycyclohexyl silylate, 6-vinyloxyhexyl (meth) acrylate, 4-vinyloxymethylcyclohexylmethyl (meth) acrylate, 3-vinyloxymethylcyclohexylmethyl (meth) acrylate, (meth) acrylic acid 2-vinyloxymethylcyclohexylmethyl, p-vinyloxymethylphenylmethyl (meth) acrylate, m-vinyloxymethylphenylmethyl (meth) acrylate, o-vinyloxymethylphenylmethyl (meth) acrylate, (meth) 2- (vinyloxyethoxy) ethyl acrylate, 2- (vinyloxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxy) propyl (meth) acrylate, 2- (vinyloxy) (meth) acrylate Ethoxy) isopropyl, (meth) acrylic acid 2- Vinyloxyisopropoxy) propyl, 2- (vinyloxyisopropoxy) isopropyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyisopropoxy) (meth) acrylate ) Ethyl, 2- (vinyloxyisopropoxyethoxy) ethyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) ethyl (meth) acrylate, 2- (vinyloxyethoxyethoxy) propyl (meth) acrylate 2- (vinyloxyethoxyisopropoxy) propyl (meth) acrylate, 2- (vinyloxyisopropoxyethoxy) propyl (meth) acrylate, 2- (vinyloxyisopropoxyisopropoxy) propyl (meth) acrylate, (Meth) acrylic acid 2- (vinylo) Xylethoxyethoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyethoxyisopropoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyisopropoxyethoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyisopropoxy) Isopropoxy) isopropyl, (meth) acrylic acid 2- (vinyloxyethoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (vinyloxyethoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (isopropenoxyethoxy) ) Ethyl, (meth) acrylic acid 2- (isopropenoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (isopropenoxyethoxyethoxyethoxy) ethyl, (meth) acrylic acid 2- (isopropenoxyethoxyethoxyethoxy) D ) Ethyl, and (meth) Polyethylene glycol monovinyl ether acrylate, and (meth) acrylic acid polypropylene glycol monovinyl ether.

  Among these, since the viscosity of the ink can be further lowered, the flash point is high, and the curability of the ink is excellent, 2- (vinyloxyethoxy) ethyl (meth) acrylate, that is, 2- (vinyloxy) acrylate At least one of ethoxy) ethyl and 2- (vinyloxyethoxy) ethyl methacrylate is preferable, and 2- (vinyloxyethoxy) ethyl acrylate is more preferable. In particular, since 2- (vinyloxyethoxy) ethyl acrylate and 2- (vinyloxyethoxy) ethyl methacrylate have a simple structure and a small molecular weight, the viscosity of the ink can be significantly reduced. Examples of 2- (vinyloxyethoxy) ethyl (meth) acrylate include 2- (2-vinyloxyethoxy) ethyl (meth) acrylate and 2- (1-vinyloxyethoxy) ethyl (meth) acrylate. Examples of 2- (vinyloxyethoxy) ethyl acrylate include 2- (2-vinyloxyethoxy) ethyl acrylate and 2- (1-vinyloxyethoxy) ethyl acrylate. Incidentally, 2- (vinyloxyethoxy) ethyl acrylate is superior in terms of curability compared to 2- (vinyloxyethoxy) ethyl methacrylate.

  A vinyl ether group containing (meth) acrylic acid ester may be used individually by 1 type, and may be used in combination of 2 or more type.

  The vinyl ether group-containing (meth) acrylic acid esters, in particular, the content of 2- (vinyloxyethoxy) ethyl (meth) acrylate is 10 to 90% by mass with respect to the total mass (100% by mass) of the ink. Preferably, 20-80 mass% is more preferable, 20-70 mass% is further more preferable, and 20-60 mass% is still more preferable. When the content is 10% by mass or more, the viscosity of the ink can be reduced and the curability of the ink can be further improved. On the other hand, when the content is 90% by mass or less, the storage stability of the ink can be maintained in a good state, and the generation of curing wrinkles can be more effectively prevented.

  The method for producing the vinyl ether group-containing (meth) acrylic acid esters is not limited to the following, but is a method of esterifying (meth) acrylic acid and a hydroxyl group-containing vinyl ether (Production Method B), (meth) acrylic acid halide. And esterification of (meth) acrylic anhydride and hydroxyl group-containing vinyl ether (production method D), esterification of (meth) acrylic acid ester and hydroxyl group-containing vinyl ether Method of exchange (Production method E), Method of esterifying (meth) acrylic acid and halogen-containing vinyl ether (Method of production F), Method of esterifying alkali (earth) metal salt of (meth) acrylic acid and halogen-containing vinyl ether (Production G), hydroxyl group-containing (meth) acrylic acid ester and carboxylic acid vinyl ester How to vinyl exchange and Le (Procedure H), hydroxyl group-containing (meth) How to ether exchange and acrylic acid ester and an alkyl vinyl ether (Process I).

  Among these, since the desired effect can be further exhibited in this embodiment, the production method E is preferable.

(Polymerizable compounds other than the above)
As the polymerizable compound other than the above (hereinafter, referred to as “other polymerizable compound”), conventionally known various monomers and oligomers such as monofunctional, bifunctional, and trifunctional or more polyfunctional can be used. . Examples of the monomer include unsaturated carboxylic acids such as (meth) acrylic acid, itaconic acid, crotonic acid, isocrotonic acid and maleic acid, salts or esters thereof, urethane, amide and anhydride thereof, acrylonitrile, styrene, various types Unsaturated polyesters, unsaturated polyethers, unsaturated polyamides, and unsaturated urethanes. Examples of the oligomer include oligomers formed from the above monomers such as linear acrylic oligomers, epoxy (meth) acrylate, oxetane (meth) acrylate, aliphatic urethane (meth) acrylate, and aromatic urethane (meth). Acrylate and polyester (meth) acrylate are mentioned.

  Moreover, an N-vinyl compound may be included as another monofunctional monomer or polyfunctional monomer. Examples of the N-vinyl compound include N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, and derivatives thereof.

  Among other polymerizable compounds, an ester of (meth) acrylic acid, that is, (meth) acrylate is preferable.

  Among the above (meth) acrylates, monofunctional (meth) acrylates include, for example, isoamyl (meth) acrylate, stearyl (meth) acrylate, lauryl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, iso Myristyl (meth) acrylate, isostearyl (meth) acrylate, 2-ethylhexyl-diglycol (meth) acrylate, 2-hydroxybutyl (meth) acrylate, butoxyethyl (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, methoxydiethylene glycol ( (Meth) acrylate, methoxypolyethylene glycol (meth) acrylate, methoxypropylene glycol (meth) acrylate, phenoxyethyl (meth) acrylate , Tetrahydrofurfuryl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, lactone-modifiable Examples include flexible (meth) acrylate, t-butylcyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, and benzyl (meth) acrylate. Among these, at least one selected from the group consisting of phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, and isobornyl (meth) acrylate is preferable.

  Among the above (meth) acrylates, examples of the bifunctional (meth) acrylate include diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, and polyethylene glycol di (meth). Acrylate, dipropylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) Acrylate, 1,9-nonanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol-tricyclodecane di (meth) acrylate, bisphenol A EO ( Tylene oxide) adduct di (meth) acrylate, PO (propylene oxide) adduct di (meth) acrylate of bisphenol A, neopentyl glycol di (meth) acrylate hydroxypivalate, and polytetramethylene glycol di (meth) acrylate Can be mentioned. Among these, dipropylene glycol di (meth) acrylate is preferable.

  Among the above (meth) acrylates, trifunctional or more polyfunctional (meth) acrylates include, for example, trimethylolpropane tri (meth) acrylate, EO-modified trimethylolpropane tri (meth) acrylate, and pentaerythritol tri (meth) acrylate. , Pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate, glycerin propoxytri (meth) acrylate, cowprolactone modified trimethylolpropane tri (meth) acrylate, pentaerythritol Examples include ethoxytetra (meth) acrylate and caprolactam-modified dipentaerythritol hexa (meth) acrylate.

  Among these, the ink in the present embodiment preferably includes at least one of a monofunctional (meth) acrylate and a bifunctional or higher (meth) acrylate because the following advantageous effects are obtained. It is more preferable that monofunctional (meth) acrylate is included, and it is further more preferable that both are included. In this case, the viscosity of the ink is low, the photopolymerization initiator and other additives are excellent in solubility, discharge stability during ink jet recording is easily obtained, and the toughness, heat resistance, and chemical resistance of the coating film are high. Increase. Moreover, since it is more excellent in curability and initiator solubility, among monofunctional (meth) acrylates, phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, 2-hydroxyphenoxypropyl (meth) acrylate, and phenoxydiethylene glycol ( Monofunctional (meth) acrylates having an aromatic ring skeleton in the molecule, such as (meth) acrylate, are preferred. Further, in order to further improve the curability and the abrasion resistance of the coating film, among the bifunctional or higher (meth) acrylates, diethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, and dipropylene glycol di ( One or more selected from the group consisting of (meth) acrylates are preferred.

  The said other polymeric compound may be used individually by 1 type, and may use 2 or more types together.

  When the other polymerizable compound is included, the content is preferably 5 to 85% by mass and more preferably 15 to 70% by mass with respect to the total mass (100% by mass) of the ink. In particular, the content of monofunctional (meth) acrylates excluding the above-mentioned vinyl ether group-containing (meth) acrylic acid esters is more excellent in curability, viscosity reduction, and storage stability due to the solubility of the photopolymerization initiator. Therefore, 5 to 50% by mass is preferable and 10 to 40% by mass is more preferable with respect to the total mass (100% by mass) of the ink. Moreover, since content of bifunctional or more (meth) acrylate becomes what was further excellent in sclerosis | hardenability, abrasion resistance, and adhesiveness, 5-55 mass with respect to the total mass (100 mass%) of an ink. % Is preferable, and 10 to 40% by mass is more preferable.

(Photopolymerization initiator)
The ink in this embodiment may further contain a photopolymerization initiator. The photopolymerization initiator is used to form a print by curing the ink present on the surface of the recording medium by photopolymerization by ultraviolet irradiation. By using ultraviolet rays (UV) among ultraviolet rays, safety is excellent and the cost of the light source lamp can be reduced. There is no limitation as long as it generates active species such as radicals and cations by the energy of light (ultraviolet rays) and initiates polymerization of the polymerizable compound, but photo radical polymerization initiators and photo cationic polymerization initiators are used. Among them, it is preferable to use a photo radical polymerization initiator.

  Examples of the photo radical polymerization initiator include aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-containing compounds, etc.), α-aminoalkyls, and the like. Examples include phenone compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon halogen bond, and alkylamine compounds.

  Among these, since the ink curability can be further improved, a thioxanthone compound is preferable, and a combination of an acylphosphine oxide compound and a thioxanthone compound is more preferable.

  Specific examples of the photo radical polymerization initiator include acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine. , Carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyldimethyl ketal, 1- (4-isopropylphenyl) ) -2-Hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone, diethyl Oxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-propan-1-one, bis (2,4,6-trimethylbenzoyl) -phenyl Phosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethylthioxanthone, and bis- (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide Can be mentioned.

  Examples of commercially available photo radical polymerization initiators include IRGACURE 651 (2,2-dimethoxy-1,2-diphenylethane-1-one), IRGACURE 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173. (2-hydroxy-2-methyl-1-phenyl-propan-1-one), IRGACURE 2959 (1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane- 1-one), IRGACURE 127 (2-hydroxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl} -2-methyl-propan-1-one}, IRGACURE 907 (2-Methyl-1- (4-methylthiophenyl) -2-morphol Linopropan-1-one), IRGACURE 369 (2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1), IRGACURE 379 (2- (dimethylamino) -2-[(4- Methylphenyl) methyl] -1- [4- (4-morpholinyl) phenyl] -1-butanone), DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), IRGACURE 819 (bis (2, 4,6-trimethylbenzoyl) -phenylphosphine oxide), IRGACURE 784 (bis (η5-2,4-cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H-pyrrole-1-) Yl) -phenyl) titanium), IRGACURE OXE 01 (1.2-octanedione, 1- [4- (phenylthio)-, 2- (O-benzoyloxime)]), IRGACURE OXE 02 (ethanone, 1- [9-ethyl-6- (2-methylbenzoyl) -9H-carbazol-3-yl]-, 1- (O-acetyloxime)), IRGACURE 754 (oxyphenylacetic acid, 2- [2-oxo-2-phenylacetoxyethoxy] ethyl ester and oxyphenylacetic acid, 2- (2-hydroxyethoxy) ethyl ester mixture) (above, manufactured by BASF), Speedcure TPO, Speedcure DETX (2,4-diethylthioxanthone), Speedcure ITX (2-isopropylthioxanthone) (above, manufactured by Lambson), KAYACURE DETX-S (2 , 4-diethylthioxanthone) (manufactured by Nippon Kayaku Co., Ltd.), Lucirin TPO, LR8883, LR8970 (above, manufactured by BASF), and Ubekrill P36 (manufactured by UCB).

  The said photoinitiator may be used individually by 1 type, and may be used in combination of 2 or more type.

  5-15 mass% is preferable with respect to the total mass (100 mass%) of an ink, and, as for content of a photoinitiator, 7-13 mass% is more preferable. When the content is within this range, the ultraviolet curing rate can be sufficiently exerted, and the undissolved portion of the photopolymerization initiator and coloring derived from the photopolymerization initiator can be avoided. Among the photopolymerization initiators, an acyl phosphine oxide compound is preferably included. 5-15 mass% is preferable with respect to the total mass (100 mass%) of an ink, and, as for content of the said acylphosphine oxide compound, 7-13 mass% is more preferable.

  In addition, it is possible to omit the addition of a photopolymerization initiator by using a photopolymerizable compound as the polymerizable compound described above, but it is easier to start polymerization by using a photopolymerization initiator. It can be adjusted and is preferred.

[Color material]
The ink may further include a color material. As the color material, at least one of a pigment and a dye can be used.

(Pigment)
By using a pigment as the color material, the light resistance of the ink can be improved. As the pigment, both inorganic pigments and organic pigments can be used.

  As the inorganic pigment, carbon black (CI pigment black 7) such as furnace black, lamp black, acetylene black and channel black, iron oxide, and titanium oxide can be used.

  Organic pigments include insoluble azo pigments, condensed azo pigments, azo lakes, chelate azo pigments, etc., phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Polycyclic pigments, dye chelates (eg basic dye chelates, acid dye chelates), dyeing lakes (basic dye rakes, acid dye rakes), nitro pigments, nitroso pigments, aniline black, daylight A fluorescent pigment is mentioned.

  More specifically, as a carbon black used for black ink, No. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, no. 2200B and the like (manufactured by Mitsubishi Chemical Corporation), Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. (and above, manufactured by Columbia Columbia), Regal 400R, Rega1 330R, Rega1 660R, Mogul L, Monarch 700, Monarch 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc. (from CABOT JAPAN K. F. C. , Color Black FW2, Color Black FW2V, Color Black FW 18, Color Black FW200, Color B1ack S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, Sep, Special Black S6, Color Black S160, Color Black S160, Color Black S170, Color Black S170, Color Black S170, Color Black S170, Color Black S170 Degussa), Microlith Black 0066 K (formerly Microlith Black C-K, manufactured by BASF).

  Examples of pigments used in white ink include C.I. I. Pigment white 6, 18, and 21.

  Examples of pigments used in yellow ink include C.I. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 167, 172, 180.

  Examples of pigments used in magenta ink include C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245, or C.I. I. Pigment violet 19, 23, 32, 33, 36, 38, 43, 50.

  Examples of pigments used for cyan ink include C.I. I. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15:34, 15: 4, 16, 18, 22, 25, 60, 65, 66, C.I. I. Bat Blue 4, 60.

  Examples of pigments other than magenta, cyan, and yellow include C.I. I. Pigment green 7,10, C.I. I. Pigment brown 3, 5, 25, 26, C.I. I. Pigment orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63.

  The said pigment may be used individually by 1 type, and may use 2 or more types together.

  When using said pigment, the average particle diameter has preferable 300 nm or less, and 50-200 nm is more preferable. When the average particle diameter is in the above range, the ink can be more excellent in reliability such as ejection stability and dispersion stability, and an image with excellent image quality can be formed. Here, the average particle diameter in the present specification is measured by a dynamic light scattering method.

(dye)
A dye can be used as the coloring material. The dye is not particularly limited, and acid dyes, direct dyes, reactive dyes, and basic dyes can be used. Examples of the dye include C.I. I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. I. Acid Red 52, 80, 82, 249, 254, 289, C.I. I. Acid Blue 9, 45, 249, C.I. I. Acid Black 1, 2, 24, 94, C.I. I. Food Black 1, 2, C.I. I. Direct Yellow 1,12,24,33,50,55,58,86,132,142,144,173, C.I. I. Direct Red 1,4,9,80,81,225,227, C.I. I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. I. Directed Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. I. Reactive Red 14, 32, 55, 79, 249, C.I. I. Reactive black 3, 4, and 35 are mentioned.

  The said dye may be used individually by 1 type, and may use 2 or more types together.

  The content of the color material is preferably 1 to 20% by mass with respect to the total mass (100% by mass) of the ink because excellent concealability and color reproducibility can be obtained.

[Dispersant]
When the ink contains a pigment, a dispersant may be further included in order to improve pigment dispersibility. Although it does not specifically limit as a dispersing agent, For example, the dispersing agent currently used for preparing pigment dispersion liquids, such as a polymer dispersing agent, is mentioned. Specific examples include polyoxyalkylene polyalkylene polyamines, vinyl polymers and copolymers, acrylic polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxies. The thing which has 1 or more types of resin as a main component is mentioned. Commercially available polymer dispersants include Ajinomoto Fine Techno's Ajisper series, Solspers series (Solsperse 36000, etc.) available from Avecia and Noveon, and BYK Chemie's Dispersic series. , Disparon series manufactured by Enomoto Kasei.

[Slip agent]
The ink of this embodiment may further contain a slip agent (surfactant). The slip agent is not particularly limited. For example, polyester-modified silicone or polyether-modified silicone can be used as a silicone-based surfactant, and polyether-modified polydimethylsiloxane or polyester-modified polydimethylsiloxane is particularly used. preferable. Specific examples include BYK-347, BYK-348, BYK-UV3500, 3510, 3530, and 3570 (above, manufactured by BYK).

  A slip agent may be used individually by 1 type, and may be used in combination of 2 or more type. The content of the slip agent is not particularly limited, and a preferable amount may be added as appropriate.

[Other additives]
The ink may contain additives (components) other than the additives listed above. Such components are not particularly limited, and may include, for example, conventionally known polymerization accelerators, polymerization inhibitors, penetration enhancers, wetting agents (humectants), and other additives. Examples of the other additives include conventionally known fixing agents, antifungal agents, preservatives, antioxidants, ultraviolet absorbers, chelating agents, pH adjusting agents, and thickeners.

  Hereinafter, the embodiments of the present invention will be described more specifically by way of examples. However, the embodiments are not limited to these examples.

[Raw materials]
The raw materials used in the following examples and comparative examples are as follows.
[Color material]
Microlith Black C-K (CI Pigment Black 7, trade name manufactured by BASF, abbreviated as “black pigment” in the table below)
[Dispersant]
Solsperse 36000 (trade name, manufactured by Lubrizol Corporation, described as “SOL36000” in the table below)
[Vinyl ether group-containing (meth) acrylic acid esters]
VEEA (2- (2-vinyloxyethoxy) ethyl acrylate, trade name of Nippon Shokubai Co., Ltd., described as “VEEA” in the table below)
[Polymerizable compounds other than the above]
・ Biscoat # 192 (phenoxyethyl acrylate, trade name of OSAKA ORGANIC CHEMICAL INDUSTRY LTD., Described as “PEA” in the table below)
IBXA (Isobornyl acrylate, trade name of Osaka Organic Chemical Industry Co., Ltd., described as “IBX” in the table below)
V # 160 (benzyl acrylate, trade name manufactured by Osaka Organic Chemical Industry Co., Ltd., described as “BZA” in the table below)
SR230 (diethylene glycol diacrylate, trade name manufactured by Sartomer, described as “DEGDA” in the table below)
APG-200 (Tripropylene glycol diacrylate, trade name of Shin-Nakamura Chemical Co., Ltd., described as “TPGDA” in the table below)
(Photopolymerization initiator)
IRGACURE 819 (trade name manufactured by BASF, solid content: 100%, described as “819” in the table below)
DAROCURE TPO (trade name, manufactured by BASF, 100% solid content, described as “TPO” in the table below)
[Slip agent]
BYK-UV3500 (trade name, manufactured by BYK, described as “UV3500” in the table below)

[Examples 1 to 18, Comparative Examples 1 to 11]
(Preparation of pigment dispersion)
Prior to ink preparation, a pigment dispersion was prepared. 1.7 parts by mass of the black pigment, 0.6 parts by mass of the dispersant, and 20 parts by mass of the polymerizable compound as a dispersion medium were mixed and stirred with a stirrer for 1 hour. The mixed liquid after stirring was dispersed with a bead mill to obtain a pigment dispersion. The dispersion conditions were such that zirconia beads having a diameter of 0.65 mm were filled at a filling rate of 70%, the peripheral speed was 9 m / s, and the dispersion time was 2 to 4 hours. The dispersion medium was used up to the amount of polymerizable compound that can be used for each ink in the priority order of PEA, BZA, IBX, and VEEA.

[Preparation of UV curable ink]
The components described in Table 1 below were added so as to have the composition described in Table 1 below (unit:% by mass), and this was stirred with a high-speed water-cooled stirrer, whereby a black ultraviolet curable ink 1 To 10 were prepared.

[Inkjet recording of Example 1]
Inkjet recording was performed using the printer 1 which is the line printer of FIG. 4 described above. Specifically, the black ink head K of the printer 1 was filled with each of the ultraviolet curable inks prepared above. The nozzle density of the head was 720 dpi. On a PET film (PET50A [trade name], manufactured by Lintec Corporation) as a recording medium, a solid having a film thickness of 10 μm under the conditions of a recording resolution of 720 dpi × 720 dpi, a duty of 100%, and one pass (single pass). A pattern image was printed. The ink was printed at a heating temperature for each ink so as to be 10 mPa · s. Note that the “solid pattern image” in the present specification means an image in which dots are recorded for all of the pixels that are the minimum recording unit area defined by the recording resolution.

For the purpose of curing the image together with the above-described printing, an irradiation peak intensity of 800 mW / cm ² (the UV irradiation device installed on the downstream side in the conveyance direction of the recording medium, that is, the LED with the lens in the first irradiation unit 42b (described above)). Table 2 below), ultraviolet light having an LED input current of 120 mA (per UV-LED) and an emission peak wavelength of 395 nm was irradiated for a predetermined time. The irradiation energy at this time was 400 mJ / cm ² (see Table 2 below). Inkjet recording was performed in this way to obtain a recorded matter.

In addition, the irradiation peak intensity | strength of each Example mentioned later was adjusted by changing the input current of a LED element, and was measured by the distance from a light emission surface to a recording medium. The irradiation energy is a value calculated from the product of the irradiation peak intensity [mW / cm ² ] and the irradiation time [s]. Each of the irradiation units 42 and 44 keeps irradiating during printing, and an irradiation region in which one point of the irradiated surface of the recording medium conveyed under the irradiation unit is irradiated by the irradiation unit. The irradiation continuation time at the time of passing was set as irradiation time T1. The irradiation time T1 was adjusted by changing the number of light emitted from the plurality of UV-LEDs arranged in the recording medium conveyance direction in the irradiation unit as necessary. Other unit heads and irradiation units were not used.

[Each inkjet recording of Examples 2, 3, 7, 9, 10, 13-18 and Comparative Examples 1, 3-11]
Except that the irradiation peak intensity and irradiation energy were the values shown in Tables 2 to 4 below, inkjet recording was performed in the same manner as in Example 1 to obtain a recorded matter.

[Inkjet recording of Example 8]
Ink jet recording was performed in the same manner as in Example 1 except that the second irradiation unit 44 was used instead of the first irradiation unit 42b and the irradiation peak intensity and irradiation energy shown in Table 2 below were used, and the recorded matter was recorded. Obtained.

[Each inkjet recording of Examples 4 to 6 and Comparative Example 2]
The irradiation peak intensity and irradiation energy of the first irradiation unit 42b are set to the values shown in Tables 2 and 3 below, and the second irradiation unit 44 is used in addition to the first irradiation unit 42b, and the following Tables 2 to 2 are used. Except that the irradiation peak intensity and irradiation energy shown in 4 were used, inkjet recording was performed in the same manner as in Example 1 to obtain a recorded matter.

[Inkjet recording of Example 11]
Inkjet recording was performed in the same manner as in Example 1 except that the LED in the first irradiation unit 42b was replaced with the lens-less LED and replaced with the lens-less LED described above to obtain a recorded matter. The irradiation time T1 was the same as in Example 1. The input current of the LED required 140 mA.

[Inkjet recording of Example 12]
Ink-jet recording is performed in the same manner as in Example 1 except that the UV-LED in the first irradiation unit 42b is replaced by a lens-less LED and is a lens-less LED and the above-described pulse irradiation LED, and the ink 2 is used. And recorded matter was obtained. The pulse irradiation LED had a duty ratio of 0.5, a pulse frequency of 1 kHz, and an input current of 220 mA. The irradiation time T1 was the same as in Example 1.

[Evaluation item]
About the recorded matter obtained by each Example and each comparative example, sclerosis | hardenability, hardening wrinkles, abrasion resistance, bleed resistance, and discharge stability were evaluated with the following method.

[1. Curability test 1]
The surface of the solid pattern image (recording surface) was rubbed with Johnson cotton swab made by Johnson & Johnson with 20 reciprocations and 100 g load, and the recording surface was scratched. Judgment was made based on whether or not there was, and the curability during printing was evaluated. The evaluation criteria are as follows. The evaluation results are shown in Tables 2 to 4 below.
○: No scratch ×: Scratch

[2. Curability test 2]
Separately, each ink composition was applied to a PET film (PET50A) with a bar coater, and cured by irradiation with a UV-LED having an irradiation peak intensity of 800 mW / cm ² and an emission peak wavelength of 395 nm, and a 10 μm cured coating film. In this case, the surface was rubbed under the same conditions as in the above-described curability test 1, and the irradiation energy required until the evaluation standard became “◯” was evaluated. The evaluation results are shown in Table 1 as “ink curability”.
A: 200mJ / cm ² or less B: 200mJ / cm ² ultra 300 mJ / cm ² or less C: 300mJ / cm ² than [3. Cured wrinkles)
Using the laser microscope VK-9700 (manufactured by KEYENCE) as the surface roughness of the recording medium, the root mean square height (Rq value) was measured, and the recording surface was visually observed.
The evaluation criteria are as follows. The evaluation results are shown in Tables 2 to 4 below.
○: Rq was 3 or less. A sufficient gloss was observed when the reflected light of the film was observed.
Δ: Rq was more than 3 and 5 or less. When the reflected light from the film was seen, a slightly insufficient gloss was observed.
X: Rq exceeded 5. When the reflected light from the film was seen, the glossiness was insufficient and the surface looked rough.

[4. (Rubbing resistance)
In accordance with JIS K5701 (ISO 11628) (specifying methods for testing inks, color developed samples, and printed materials used for lithographic printing), the Gakushin friction fastness tester (TESTER SANGYO CO., LTD.) Was used to evaluate the abrasion resistance. In the evaluation method, a gold width was placed on the surface to be recorded and rubbed with a load of 400 g. After the rubbing, peeling and scratches on the cured surface of the recorded matter were visually compared.
The evaluation criteria are as follows. The evaluation results are shown in Tables 2 to 4 below.
1: There was no stain on the gold rim. There was no peeling or scratches on the printed surface.
2: Dirt of the gold width was seen. There was no peeling or scratches on the printed surface.
3: Dirt of the gold width was seen. Peeling and scratches on the printed surface were also observed.

[5. (Bleed resistance)
The edge part of the obtained solid pattern image was observed visually. The evaluation criteria are as follows. The evaluation results are shown in Tables 2 to 4 below.
1: No blur was observed at the edge of the solid pattern image.
2: Bleeding was observed at the edge of the solid pattern image.

[6. (Discharge stability)
An ink jet evaluation machine (prototype) having 180 nozzles with a discharge nozzle diameter of 20 μm, a driving frequency of 18 kHz, and an ink discharge amount per time adjusted to 11 ng was prepared. Then, using the evaluation machine, the number of nozzles in which nozzle omission occurred when ink was ejected continuously for 60 minutes was determined.
The evaluation criteria are as follows. The evaluation results are shown in Tables 2 to 4 below.
1: 1 or less 2: 2 to 4 3: 5 to 7 4: 8 or more

From the above results, the ultraviolet curable ink containing a predetermined vinyl ether group-containing (meth) acrylic acid ester is excellent in curability, and includes a discharge step including discharging the ink onto a recording medium, and the recording target. A curing method including irradiating ultraviolet rays from an ultraviolet light emitting diode having an irradiation peak intensity of 800 mW / cm ² or more to the ink landed on the medium and curing the ink (each example) It is clear that compared with other recording methods (each comparative example), it is excellent in curability, can effectively prevent curing wrinkles, and also has good abrasion resistance, ejection stability, and bleed resistance. became.

Consider the above results. From Comparative Example 1, it is presumed that when the result of curing wrinkles is bad, the abrasion resistance tends to be poor. From Example 5 and Comparative Example 2, it is estimated that even when the second irradiation is performed, the result of curing wrinkles is affected when the irradiation peak intensity in the first irradiation is less than 800 mW / cm ² . The reason why the result of the bleed resistance in Comparative Example 5 is poor is presumed to be because the curing by the first irradiation is slow. From Comparative Examples 3, 7, 8, and 11, the predetermined vinyl ether group-containing (meth) acrylic acid esters contained in the ink have excellent curability and increase the curing speed. It is presumed that the bleed resistance is also good, and even when the ink does not contain a predetermined vinyl ether group-containing (meth) acrylic acid ester, if the irradiation energy is increased to make the printing curability good. It is also speculated that cured wrinkles will be good. Note that Comparative Example 11 is not preferable because the number of UV-LEDs arranged in the transport direction of the irradiation unit 42b needs to be very large, and the heat generation of the irradiation unit is increased due to the large number of UV-LEDs. Guessed.

  Further, from Examples 3 and 11, when the irradiation peak intensity and irradiation energy of the first irradiation are very large, the viscosity of the ink in the nozzle is greatly reduced due to heat generation of the light source, and the ejection characteristics are changed. It is presumed that the ejection stability deteriorated due to the increased light leakage and the increased viscosity due to the polymerization of the ink at the nozzle. From Example 8, it is presumed that the bleed resistance tends to deteriorate when the first irradiation part does not perform irradiation. From Examples 9, 10, and 14, when the amount of the predetermined vinyl ether group-containing (meth) acrylic acid ester contained in the ink is large, curing wrinkles tend to occur slightly, while the irradiation peak intensity of the first irradiation It is presumed that generation of hardening wrinkles can be effectively prevented by making the diameter relatively large. When Example 1 and 11 are compared, when LED without a lens is used, it is estimated that it is necessary to increase the input current of the light source, and as a result, the heat generation increases, and thus the ejection stability tends to be inferior. From Examples 9 and 12, even if the LED is a lens-less LED, if the LED by pulse irradiation is used, the heat generation of the LED can be reduced by reducing the irradiation energy while increasing the irradiation peak wavelength, and the discharge stability is improved. It is estimated that it will be excellent. In addition, the inks 6 and 10 tend to be difficult to dissolve the initiator, and it is estimated that the ejection stability of Example 16 and Comparative Example 10 was inferior due to the precipitation of the initiator. The reason why the abrasion resistance of Example 18 is inferior is presumed to be that the abrasion resistance of the ink 8 is inferior.

  1 printer, 20 transport unit, 23A upstream transport roller, 23B downstream transport roller, 24 belt, 30 head unit, 40 irradiation unit, 42a, 42b, 42c, 42d, 42e first irradiation unit, 44 second irradiation unit, 50 detector group, 60 controller, 72 UV-LED, 72a UV-LED chip, 72b condenser lens, 110 computer, S recording medium, T1 Time from the start of irradiation to the end of irradiation.

Claims (9)

A discharge step including discharging an ultraviolet curable ink containing a vinyl ether group-containing (meth) acrylic acid ester represented by the following general formula (I) onto a recording medium;
A curing step including irradiating the ultraviolet curable ink landed on the recording medium with ultraviolet rays from an ultraviolet light emitting diode having a peak intensity of ultraviolet rays of 800 mW / cm ² or more, and curing the ink; An ink jet recording method comprising:
_{^{CH 2 = CR 1 -COOR 2 -O}} -CH = CH-R 3 ··· (I)
(In the formula, R ¹ is a hydrogen atom or a methyl group, R ² is a divalent organic residue having 2 to 20 carbon atoms, and R ³ is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms. Group.) The inkjet recording method according to claim 1, wherein the irradiation energy of ultraviolet rays emitted from the ultraviolet light emitting diode is 100 to 600 mJ / cm ² . In the curing step, before irradiating ultraviolet rays from the ultraviolet light emitting diode having a peak intensity of 800 mW / cm ² or more, the emission peak wavelength is in the range of 360 to 420 nm, and the peak intensity of the irradiated ultraviolet rays is 800 mW. The method according to claim 1, further comprising: irradiating an ultraviolet ray having an irradiation energy of 50 mJ / cm ² or less from an ultraviolet light emitting diode that generates an ultraviolet ray that is less than / cm ² to temporarily cure the ultraviolet curable ink. The inkjet recording method as described.   The inkjet recording method according to any one of claims 1 to 3, wherein recording is performed using a line inkjet recording apparatus including a line head having a length equal to or longer than a width of a recording medium.   5. The inkjet recording method according to claim 1, wherein the irradiation from the ultraviolet light emitting diode is independently at least one of pulse irradiation and spot irradiation by a condenser lens. 6. The inkjet recording method according to claim 1 or 2, wherein a peak intensity of the irradiated ultraviolet ray is in a range of 800 to 4,000 mW / cm ² .   The inkjet recording method according to claim 1, wherein the ultraviolet light emitting diode has an emission peak wavelength in a range of 360 to 420 nm.   The ultraviolet curable ink used for the inkjet recording method of any one of Claims 1-7.   An ink jet recording apparatus using the ink jet recording method according to claim 1.